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What Happens When the Transponder Dies?

By Edited Sep 17, 2016 0 0

It was a beautiful day yesterday, and we flew circuits for a bit. Halfway through something happened.

Tower directed  me to reset the transponder, because it had stopped showing up. (This isn’t as bad as it seems, because I was still on radar – they had me on radar, so they were only missing my altitude, and since I was in the circuit they knew what that was).

Anyway, I tried it and asked them if it was working and it was gone. Tower told me to check it out when I landed.Lucky for me, one of my partners fixes transponders.

What I thought was going to be a big deal wasn't a problem at all.

The first job is taking the transponder out. If you’re only experience is installing car stereos, a NARCO AT 150 is a treat.


The transponder is the unit at the bottom, and you’ll see there is a little hole on the bottom right of it right under the IDENT button.


Guess what? An Allan key fits right inside.

It loosens a long screw that attaches the instrument to the plane. You can see how nicely it slides out. Not at all like my ’72 Toyota Celica with the AM/FM 8 track.

NARCO AT150(41661)

You can see the attachment point at the end of the mounting box, along with the connector.

NARCO AT150(41662)

No wire harness or plug. Instead, it connects just like a card in a computer.


NARCO AT150(41663)

Once it was out we threw it on a few testers. No problem. We cleaned the connector with alcohol and re-installed it. I powered it up, waited a bit for the tube inside to warm up, but no use!Of course, there was something simple I should have thought of in the first place, possibly while in the air – the fuse. I pulled it, inspected it and found nothing wrong. I replaced it and you know it, the transponder light blinked blue. Back in business!What happened? Gremlins?Of course not. Remember, I was flying circuits on my way to soloing. Take off, turn out, do the downwind check “Primer in and locked, masters on, mags both, fuses and circuit breakers in….”And that’s when I created the problem in the first place. Running my hands over the fuses must have been the cause. I won't do that again, and if I have another non-critical electrical malfunction I’ll be sure to check the fuses right away. 


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